Second-site capsule-locus mutations, not Ade efflux disruption, determine phage susceptibility across an Acinetobacter baumannii transposon mutant panel

Capsule-locus mutations in AB5075 transposon mutants, not AdeABC/AdeFGH/AdeIJK efflux disruption, most strongly correlate with phage susceptibility across five Acinetobacter baumannii phages.

• Why it matters: RND efflux pumps were proposed to act as phage adsorption receptors, but genotype–phenotype links in transposon mutant panels can be confounded by unverified second-site changes.
• What they did: The study tested five phages (Equilibrator, Taro, AT01, BB02, AC03) on 13 Acinetobacter baumannii strains, using efficiency-of-plating and host-range assays plus capsule density measurements and whole-genome sequencing of nine AdeABC/AdeFGH/AdeIJK mutants.
• The result: Ade disruption did not match restricted host ranges, while sequencing found KL25 capsule-locus changes in six of ten AB5075 mutants; AC03 formed plaques on all six capsule-altered strains but none of five without them.

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